The present invention is directed to a railroad tank car specifically designed to permit the dual functions of pressure and gravity discharge of dry bulk commodities.
It has heretofore been proposed to construct a railroad tank car of a cylindrical cross-section with a fall from the ends to a central bottom outlet. Aeration of the product was accomplished by lining the bottom half of the car with a series of canvas hoses strapped to the bottom. The car was somewhat of a plumber's nightmare and was very expensive to manufacture. In addition, it was vertually impossible to clean the car with any degree of economy, and maintenance presented an horrendous problem. Due to the difficulty in maintaining cleanliness, the car was obviously unsuitable for food service. The one advantage that such a car possessed was it could be operated as either a pressure differential car or could be unloaded by gravity by merely fluidizing the layer of material in contact with the aeration system.
It is quite obvious that in designing the above car the main object was to simplify the structural problem of retaining pressure in the car body and then to equip the car with aeration devices and controls to suit this geometric configuration. By simplifying the structural approach, the car had become much more complex and expensive. In contrast, in designing the car of the present invention the geometry of the car was specifically designed to fit the requirements of the aeration devices and controls. This resulted in the car body geometry being completely defined prior to the start of the structural design.
In conceiving the design of the present invention the starting point was the provision of two inclined fluidized bed conveyors on either side of the outlet with a 10 degree slope. To ensure that any material above the conveyors would fall on to the conveyors it was necessary to provide steeply sloping sides. To retain pressure within the car body the top ends of these side sloping surfaces were closed using a segment of a circle. If the top of the car body was to remain horizontal the car body would have to be larger in diameter at the middle than at the ends, thus, the curved part of the car body was formed as an asymmetric truncated cone. This configuration had the distinct advantage that the conveyors would be relatively narrow and therefore could be installed in segments which, for cleaning purposes, could be removed through the manways in the top of the car body. Upon removal of the aeration devices, the inside of the car body could be completely cleaned. Further, by keeping the area of the aeration devices down, the cost was kept controllable since the cost of the porous metal used in the conveyors is very high. With the basic geometrical body shape determined, it was then necessary to structurally design the car to withstand train loads in a practical and economic manner.